Petroleum deposits occurring in various geological structures throughout the world are principally composed of literally thousands of hydrocarbon compounds; hence petroleum products can vary greatly with respect to their chemical and physical properties. Nonetheless, virtually all petroleum produced at a profit has had one property in common--it is "liquid" at ambient temperatures. Hence it can be pumped from those subterranean formations where it is usually found.
In a few cases however, some "immobile" (solid and/or extremely viscous), and hence "intractable", petroleum deposits have been profitably recovered. Perhaps the most notable intractable petroleum deposit which has been recovered at a profit is Trinidad Lake Asphalt. This circumstance is largely due to this deposit's accessibility at the earth's surface. However, in most cases, intractable petroleum resources are located in deep subterranean formations and commercial recovery is not feasible at current petroleum prices because virtually the entire economic value of such intractable petroleum is vitiated by its high production and processing costs. Examples of such subterranean intractable petroleums are oil shale, South American Boscan crude, the La Brea Tar Pits and the heavy Santa Maria crude deposits found in extensive regions of California.
The most costly items associated with past attempts to recover such intractable, subterranean petroleum are: (1) the considerable expense of generating the enormous quantities of steam used to melt and/or reduce the viscosity of such petroleum deposits in situ, (2) the need for large volumes of expensive cutter stocks (diluents used to thin the viscosity of the petroleum produced by melting the intractable petroleum with steam), and (3) the prohibitively high costs and technical difficulties associated with conveying intractable petroleum/diluent mixtures to distant oil refineries.
In most cases conveying intractable petroleum mixtures from a well site to a refinery involves the use of pipeline systems. They are used, whenever possible, to avoid small batch costs generally associated with rail or truck transportation. However, pipelining activities with respect to intractable petroleum have produced a host of problems. Most of them follow from the fact that high pressure drops are encountered and/or high temperatures are required to pump such mixtures. Thermal expansion and, hence, leaks, odors, spills, etc. are ever present considerations. It might also be added that movement of such intractable crudes also involves significant overhead expenses which must be incurred in order to satisfy the many laws and regulations concerned with public and environmental protection. Consequently, literally billions of barrels of petroleum resources cannot be profitably recovered by currently known production methods and, for the most part, government subsidy of one kind or another is usually needed to bring such intractable petroleum to the marketplace.
Again, the most widely used methods employed by the prior art in trying to recover such intractable petroleum economically has involved the injection of steam into such subterranean formations in order to first melt the intractable petroleum. Hence, most attempts to recover such intractable crudes involve the construction of very expensive on-site steam production facilities. Typically as much as 2,000 lbs. of steam are needed to recover one barrel of petroleum from such deposits. Such steam requirements imply that the cost of the steam used to recover this already poor quality petroleum can represent as much as one-third of its economic value when it is delivered to the refinery.
The melted petroleum is then exposed to the solvent action of a thinning oil (commonly referred to as "cutter stock") so that the resulting mixture can be forced out of the petroleum formation by use of injection and recovery well systems well known to this art. Large quantities of such cutter stocks are needed to bring the melted petroleum to the earth's surface. Thereafter, even more cutter stock is needed to provide the decreased viscosity needed to pump intractable petroleum to a conventional refinery. For example, it typically takes about one-fifth to one-quarter barrel of an already refined and expensive cutter stock such as kerosine or gas oil in order to render mobile one barrel of intractable petroleum. The cutter stock must then be re-refined along with the intractable petroleum. This requirement accounts for the loss of another major fraction of the intractable petroleum's economic value.
Again, the prior art has employed many different chemical species as "cutter stocks", "injection fluids", etc. The fluids employed in the processes taught by U.S. Pat. Nos. 2,104,327; 4,007,785, and 4,514,283 are more or less representative of such cutter stocks. For example, U.S. Pat. No. 2,104,327 ("the 327 patent") teaches the use of gas oil as a cutter stock (i.e., as an injection fluid in this particular process). It should be noted, however, that for all the reasons noted in later portions of this patent disclosure, the "gas oil" taught in the 327 patent should not be regarded as being the same material as the "medium/heavy cracked gas oil" employed in applicant's process. There are many technical distinctions between gas oil and medium/heavy cracked gas oil which will be made during the course of the development of this patent disclosure; but for the present purposes of describing the state of the prior art with respect to such cutter stocks/injection fluids, suffice it to say that the gas oil disclosed in the 327 patent is a very significant, naturally occurring, constituent of "light" crude oils. It is not, however, a constituent of intractable petroleum. That is to say that gas oil is recovered at a petroleum refinery where light crude oils are normally processed. In fact, it could be said that solid (intractable) petroleum deposits are "solid" for the very reason that they lack those lighter components such as gas oil which would otherwise endow them with the liquid (tractable) characteristics which would, in turn, make them easily recoverable by conventional oil recovery methods. In any case, if gas oils are used as injection fluids to recover intractable petroleum, they would have to be hauled from the refinery to the site of the injection well. Moreover, since gas oils are "lighter fractions" of light crude oils, they would tend to be more valuable than the heavier fractions (which incidentally could, after catalytic cracking, well include medium/heavy cracked gas oils) of these same "light" crude oils.
It should also be noted in passing that, since intractable petroleum does not contain any significant amounts of gas oil, no amount of a hereinafter described process known as "visbreaking" (i.e., thermal cracking, at very low severities of cracking conditions), applied to intractable petroleum will produce gas oils. They simply are not there for such production. In other words, the only way one might get gas oils from a solid, intractable petroleum would be to catalytically crack it under those very severe conditions (high temperatures, low pressures, long residence times, in the presence of specialized catalyst, etc.) which can only be produced by full scale, oil refinery catalytic cracking units in order to break and reform the molecular structure of certain "heavy" molecules (e.g., those of asphaltenes having molecular weights up to 20,000) into much, much "lighter" molecules. Here again, such materials would have to be hauled from a refinery to an injection used to recover the intractable petroleum.
U.S. Pat. No. 4,007,785 ("the 785 patent") teaches recovery of viscous petroleum by injection of a carefully "designed", multiple-component, solvent for recovering viscous petroleum. At least one of the "designed" solvent's components is normally a gaseous material selected from the group consisting of methane, ethane, propane or butane and at least one of the solvent's components is normally a liquid such as pentane. It should be noted, however, that the solvent used in process of the 785 patent is heated and, since it is comprised in large part of lighter hydrocarbon components, it must be therefore pressurized in order to keep it in the liquid state needed to pump the fluid into an injection well.
The economics of the process taught by the 785 patent should also be taken into consideration. For example, at today's prices, the pentane component of the "designed" injection fluids taught by the 785 patent is almost twice as valuable as gasoline. These relative values also should be compared to the gas oils taught in the 327 patent--they are about comparable in value to gasoline. Even more important, however, is the fact that all of the injection fluid ingredients taught by the 785 patent and by the 327 patent are only found "at" a refinery and hence must be hauled to the site of the injection well.
The 785 patent does suggest that its solvents are so "light" they could be recovered by thermal distillation at the oil recovery site; however, the 785 patent also clearly teaches that the highest and best use of such lighter fractions in this particular process, is to use them as a carrier or cutter stock which is needed to pipe the viscous petroleum to a distant refinery. This reference states "if the viscous petroleum is to be subjected to some form of cracking in a processing unit located some distance from the production point, all or a portion of the normally liquid hydrocarbon solvent may be allowed to remain in the viscous crude to facilitate transportation thereof in a pipeline to the cracking unit. This is especially true in the instance of applying this process to tar sands, since bitumen is much too viscous to pump in its natural form."
U.S. Pat. No. 4,514,283 ("the 283 patent") teaches a process whereby viscous asphaltenic crude oils can be converted to "pumpable" liquid oil products, in field locations, by precipitating it with 100 volumes of pentane. Again pentane is an expensive ingredient--it is about twice as expensive as gasoline--whose 100 volume requirement would make for very great economic costs. Moreover, the 100 volumes of pentane would have to be hauled to the field. The process of the 283 patent also calls for (1) separation of the crude oil's asphaltene components, (2) mildly thermally converting the asphaltenes to mobile asphaltene--conversion products (by heating them to 660.degree. F. for 1 to 3 days) and then (3) mixing the resulting asphaltene conversion products with select components of the original crude oils in order to "form a liquid oil product which can be readily pumped through pipelines."
Moreover, in addition to the costs of overcoming the technical obstacles previously noted, there also exists other non-technical, but ever present, economic dictates which permeate the petroleum industry from one end to the other That is to say the costs associated with the above noted technical difficulties reverberate through the economics of all subsequent production, transportation, refining, and marketing activities. Similar purely economic considerations also tend to discourage even the exploration which might be specifically aimed at discovering intractable petroleum resources. It should also be noted that many of the economic limitations associated with this type of petroleum follow from the simple fact that intractable petroleum, even after it is recovered, has an inherently lower economic value than lighter crudes owing to its generally heavier composition. Hence, it is inherently more expensive to refine. Overall, it yields smaller amounts of distillate products and it generally requires substantially more self-consumption of its energy value in order to carry out those subsequent operations needed to process an intractable petroleum into marketable motor fuels, heating oils, petrochemicals, etc. As a final note, it might even be said that, in many cases, a large part of the economics associated with such materials, at the oil refinery, is a reflection of the fact that a predominance of heavy, nonvolatile fractions often can bring about near distress price situations at the refinery.
In response to all of the above noted technical and/or economic problems associated with the recovery of intractable petroleum, applicant has developed processes which permit far more efficient, and hence far more economical, recovery and use of intractable petroleum. However, before going into the details of these processes, it will be helpful to define and/or comment upon certain terms used in this patent disclosure. That is to say that a number of the words and terms used to develop the scope of this patent disclosure may be employed in some special sense used in the petroleum industry, rather than in a potentially more broad sense normally associated with common English usage. Therefore, in the interest of clarity and precision, certain terms having common English meanings, as well as certain special terms, are defined in the following Glossary as an aid to understanding the ensuing portions of this patent disclosure.